Growth of CBD-In2S3 buffer layer for CIGS solar cells and the effect of annealing on its properties

Abstract

Over the last decade a substantial research effort has been concentrated on In2S3 buffer layer as alternative to conventional CdS buffer for CIGS solar cells( (1), (2)). The high efficiency was shown on a solar cell based on low band gap CIGS absorber (1.16 eV) with low band gap (~2 eV) In2S3 buffer (3). In our previous studies we have shown that the application of wide band gap chemical bath deposited (CBD) In2S3 buffer layer results in a low device efficiency, which is consistent with an unfavorable electronic structure at the ZnO/CBD-In2S3/CIGS heterointerfaces (4). It is known that the chemical composition of In-compounds affects the value of band gap, and, therefore, the interface electronic structure. The fundamental photovoltaic (PV) parameters of CIGS device are influenced by the optical, electrical and structural properties of buffer layer, as well as by the defect structure it creates with absorber. In this regard the effect of post-deposition annealing on these properties is of great importance. The annealing is especially important for chemical bath deposited film, because of its influence on the chemical composition of the film. The published experimental data on the annealing effect on the performance of CBD-In2S3 based solar cells does not provide clear understanding of the phenomenon (5).

This research is aimed to improve the quality of the In2S3 film grown by CBD. For this purpose we investigated the effect of annealing on the optical, electrical, and structural properties of In2S3 buffer layer grown by CBD method. The study, on how the annealing affects the defect structure at the CIGS absorber/In2S3 buffer interface and how it influences PV parameters of the completed solar cell, was also conducted. The optimal parameters for post-deposition annealing were deduced.

In2S3 buffer was used as alternative to the CdS in the conventional CIGS device configuration. The buffer layer was grown on soda-lime glass, ITO and CIGS substrates by CBD. CI...